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Determination of motor threshold using visual observation overestimates transcranial magnetic stimulation dosage: safety implications.

Publication ,  Journal Article
Westin, GG; Bassi, BD; Lisanby, SH; Luber, B
Published in: Clin Neurophysiol
January 2014

OBJECTIVE: While the standard has been to define motor threshold (MT) using EMG to measure motor cortex response to transcranial magnetic stimulation (TMS), another method of determining MT using visual observation of muscle twitch (OM-MT) has emerged in clinical and research use. We compared these two methods for determining MT. METHODS: Left motor cortex MTs were found in 20 healthy subjects. Employing the commonly-used relative frequency procedure and beginning from a clearly suprathreshold intensity, two raters used motor evoked potentials and finger movements respectively to determine EMG-MT and OM-MT. RESULTS: OM-MT was 11.3% higher than EMG-MT (p<0.001), ranging from 0% to 27.8%. In eight subjects, OM-MT was more than 10% higher than EMG-MT, with two greater than 25%. CONCLUSIONS: These findings suggest using OM yields significantly higher MTs than EMG, and may lead to unsafe TMS in some individuals. In more than half of the subjects in the present study, use of their OM-MT for typical rTMS treatment of depression would have resulted in stimulation beyond safety limits. SIGNIFICANCE: For applications that involve stimulation near established safety limits and in the presence of factors that could elevate risk such as concomitant medications, EMG-MT is advisable, given that safety guidelines for TMS parameters were based on EMG-MT.

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Published In

Clin Neurophysiol

DOI

EISSN

1872-8952

Publication Date

January 2014

Volume

125

Issue

1

Start / End Page

142 / 147

Location

Netherlands

Related Subject Headings

  • Young Adult
  • Transcranial Magnetic Stimulation
  • Patient Safety
  • Observation
  • Neurology & Neurosurgery
  • Motor Cortex
  • Middle Aged
  • Male
  • Humans
  • Fingers
 

Citation

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Westin, G. G., Bassi, B. D., Lisanby, S. H., & Luber, B. (2014). Determination of motor threshold using visual observation overestimates transcranial magnetic stimulation dosage: safety implications. Clin Neurophysiol, 125(1), 142–147. https://doi.org/10.1016/j.clinph.2013.06.187
Westin, Gregory G., Bruce D. Bassi, Sarah H. Lisanby, and Bruce Luber. “Determination of motor threshold using visual observation overestimates transcranial magnetic stimulation dosage: safety implications.Clin Neurophysiol 125, no. 1 (January 2014): 142–47. https://doi.org/10.1016/j.clinph.2013.06.187.
Westin, Gregory G., et al. “Determination of motor threshold using visual observation overestimates transcranial magnetic stimulation dosage: safety implications.Clin Neurophysiol, vol. 125, no. 1, Jan. 2014, pp. 142–47. Pubmed, doi:10.1016/j.clinph.2013.06.187.
Journal cover image

Published In

Clin Neurophysiol

DOI

EISSN

1872-8952

Publication Date

January 2014

Volume

125

Issue

1

Start / End Page

142 / 147

Location

Netherlands

Related Subject Headings

  • Young Adult
  • Transcranial Magnetic Stimulation
  • Patient Safety
  • Observation
  • Neurology & Neurosurgery
  • Motor Cortex
  • Middle Aged
  • Male
  • Humans
  • Fingers